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Abstract

Imaging objects embedded within highly scattering media by coupling light and ultrasounds (US) is a challenging approach. In deed, US enable direct access to the spatial localization, though resolution can be poor along their axis (cm). Up to now, several configurations have been studied, giving a millimetric axial resolution by applying to the US a microsecond pulse regime, as is the case with conventional echography. We introduce a new approach called Acousto-Optical Coherence Tomography (AOCT), enabling us to get a millimetric resolution with continuous US and light beams by applying random phase jumps on US and light. An experimental demonstration is performed with a self-adaptive holographic setup containing a photorefractive GaAs bulk crystal and a single large area photodetector.

(a) Numerical simulation of the autocorrelation function f (z) of ejφT (z) for a US phase modulation sequence with N=512 random (0,π) jumps within Tj=1 ms. The typical shape is a triangle of δz=vUStj⋍3 mm in width at half maximum.(b) Schematic representation of the coherence slice along the US beam.

(a) Acousto-optic 2D-profile of an optical absorber (x×y×z=3×7×3 mm3) embedded within a scattering gel (µ′s=6 cm-1, thickness=3 cm) performed with a random phase sequence of z=2.85mmaxial resolution. Note that the 2D profile (x, y) is orthogonal to the longitudinal axis of the light diffusion ”banana”, and to the absorbing sample cylinder axis (y). As a consequence, the image is nearly symmetric by rotation. (b) Cut along the white dashed line axis of Fig.3a.